diff --git a/src/core/workspace.c b/src/core/workspace.c
index 62328ad31..002ee8e56 100644
--- a/src/core/workspace.c
+++ b/src/core/workspace.c
@@ -369,10 +369,11 @@ void
 meta_workspace_add_window (MetaWorkspace *workspace,
                            MetaWindow    *window)
 {
+  g_return_if_fail (g_list_find (workspace->mru_list, window) == NULL);
+
   COGL_TRACE_BEGIN_SCOPED (MetaWorkspaceAddWindow,
                            "Workspace (add window)");
 
-  g_assert (g_list_find (workspace->mru_list, window) == NULL);
   workspace->mru_list = g_list_prepend (workspace->mru_list, window);
 
   workspace->windows = g_list_prepend (workspace->windows, window);